wave piercing bow topped with flared bow?

Discussion in 'Boat Design' started by Squidly-Diddly, May 24, 2020.

  1. Squidly-Diddly
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    Squidly-Diddly Senior Member

    wave pirceing bow.jpg

    I'd call it a semi-piercing duplex bow. I guess its supposed to pierce the small waves while retains normal bow flare as backup so the big waves don't wash the crew overboard. Looks like a retractable sonar strut instead of big over-size bulb.

    This Italian navy "PPA" ship has 3 levels of power. Small motors on the gear box, diesel for cruise and GTs for speed.
     
    Last edited: May 24, 2020
  2. Ad Hoc
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    Ad Hoc Naval Architect

    It is just a simple way to add waterline length - which lowers resistance - as well as a location of 'sensitive' sonar epqt etc.
    Also depending upon it's nominal speed range etc, it may assist in pressure reduction at the bow - which also can lower resistance.

    Beyond that - it is a simple 'fashion' accessory.
     
  3. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I'd have to see it in action along a normal bow, but I'm imagining it piercing waves and the upper flair only has to deflect the little bit that comes over the top of lower bow, instead of normal flaired bow that sends up the entire wave in spray.

    Maybe it wont impart as much upward force as normal bow when hitting a really big wave, but the force will be spread over more time and over more of the scanting.

    At any rate, I've made sure it was heavily re-enforced for a ramming attack. You never know when all the fancy guided missiles and radar aimed guns are gonna go on the fritz.
     
  4. Ilan Voyager
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    Ilan Voyager Senior Member

    It's not exactly a wave piercing bow. It's a reminiscence of a polyhedric bow, but not very exact as it has not the same negative facettes. I did not know that the Italian Navy design office was inspired by this so frenchie polyhedric bow.
    The Italians must have worked hard on that and found it enough interesting for a serie of 10 frigates. Generally, european navies do not risk an hazardous and unproven solution on so many boats having a life of 25 to 30 years, so I presume that works as they wanted.
    About this 143 meters ship, a very modern one with a sophisticated propulsion
    Paolo Thaon di Revel-class offshore patrol vessel - Wikipedia https://en.wikipedia.org/wiki/Paolo_Thaon_di_Revel-class_offshore_patrol_vessel

    The polyhedric bow has been created in 1994 by Pantocarene, a well known and versatile NA office in France, with Didier Marchand a very prolific and able NA.
    This bow is used by him since 25 years in a variety of boats from fishing, small ferries, pilot boats to pretty fast above 40 knots small patrol boats.
    It's a bit more than a fashion bow as it has proven largely to be efficient at least on boats from 25 to 85 feet Marchand has designed.
    A description in French
    Étrave polyédrique — Wikipédia https://fr.wikipedia.org/wiki/%C3%89trave_poly%C3%A9drique
    A video on a pilot boat Orca 1998
    Vedette de mer ORCA https://www.pilotagegironde.com/index.php/albums/videos/videos-vedettes/vedette-de-mer-orca
    A pic of the 2015 SNSM rescue boat all weather self-righting designed by Pantocarene. Composite 16mx4.6m 20 tons 500HP X 2, 26 knots, able to keep 18 knots in sea state 7, and 15 in state 9 as I have been said. They have made extensive trials in real conditions at the "Passage du Fromveur". It's after these trials in different sea states and waves that the boat has been adopted. Nothing better than trials in real conditions. Cost 1 million USD.
    [​IMG]


    A video showing a trial of self-righting, that permits to discover the beautiful water lines and more of the rescue boat.


    If you ask yourself how looks the sea in the Passage du Fromveur in a winter storm , a little video showing a frigate of 140 m long and 42 m above the water crossing it. It's a good place for sea trials in bad weather.
    https://www.dailymotion.com/video/xpw93t
     
    Last edited: May 24, 2020
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  5. Ilan Voyager
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    Ilan Voyager Senior Member

    Fishing boat Rorcal R121S3 made in composite by Sibiril Technologies shipyard.


    [​IMG]

    [​IMG]
     
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  6. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I like the flat top of ship's ram bow. I'm thinking on a smaller boat with neg camber it could be nice place to cut-in some footholds without any reduction in performance.
     
  7. bajansailor
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    bajansailor Marine Surveyor

  8. Ad Hoc
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    Ad Hoc Naval Architect

    Unfortunately there is still so much 'mythology' about wave piercing bows or reverse bows etc. None of which is supported by hydrodynamics and naval architecture.

    This type of questions have been posed endless, and the basics of understanding are described HERE regrading the effects of pitching and HERE, noting the effects merely adding waterline length, and a more general discussion explaining the overall basics in a simple Q&A HERE.

    Which is also supported bye endless research we have done summarised here too:

    upload_2020-5-26_13-41-26.png

    We tried endless different types/sizes of bow extensions - ala wave piercing bow - and you can note the difference in pitch angle and vertical acceleration to the naked hull.
    Zip.

    These tests were conducted in the large 240m Haslar tank.

    So others like to "think" or "feel" a difference. Great - but it is not supported by any evidence.

    However, when you get into the shorted and heavy hulls... is there a difference - yes -, but it is only because you're increasing the waterline length. The increase in viscous damping and changes to the moment of inertia of the waterplane are insufficient on their own, simple maths and analysis of the factors governing the equations of motion clearly support that too. As noted in those old threads, as examples.

    Thus, many use them as "fashion" statements of having something "new" or "radical" ..or for some... something "patent-able" as a major breakthrough in resistance/seakeeping.
    If you wish to believe the hype... go ahead, that's your prerogative... but it is just adding waterline length which increases the LD ratio whgich lowers resistance and which has the secondary knock on effect of lowering vertical accelerations, as it does for any hull, with or without a bow extension. Nothing fancy at all...
     
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  9. jehardiman
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    jehardiman Senior Member

    It's a warship...so it's a ram....
    Anyway, I concur it is just to increase LWL. I think a lot of people forget that Italy has an entire different strategic naval situation than the rest of Europe or the US. The Mediterranean is not the North Sea or the Atlantic, so you really don't have to build all your ships for NATO high latitude operations. With the Italian peninsula sticking out into the middle of the relatively calm Med with many miles of coastline, you can start playing with the design space more than say the US or UK.
     
  10. Ilan Voyager
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    Ilan Voyager Senior Member

    AD HOC you're totally right at least on a 50 meters catamaran which has already rather thin hulls.
    On a far shorter and wider monohull I guess (and only guess) that the polyhedric bow has a softer passage through the wave with less resistance. At least it's what say the professional users of these professional small boats since 25 years.
    Marchand has no fancy claims about his polyhedric bow, it's not the style of this NA who works essentially on rather small professional boats for local people, a domain where fancy advertising and superlative claims are totally useless. I doubt highly he has patented it, it's not the style. He uses it since 1994, probably well before the Estonians.
    He keeps the features that works on his designs, making constant improvements on each new design. He is very careful on the placement of the centers and he has his own "recipes" from his long experience. He is a provincial NA for his local customers mainly fishermen and harbor pilots. He is not interested in yachting nor in fashion design. He is a simple NA in his deep Brittany office working with local shipyards.
    He draws his boats with one assistant and uses the services of external consultants if needed. His faithful customers are happy, the boats do nicely their job and he has work for many years. Good sign his customers come back. I do not think he bothers a lot about theories.
    His pilot boats are very appreciated by the harbor pilots of Bordeaux, Saint Nazaire, Le Havre and others who uses them all year around in all weather. These 17 meters boats can keep good speed in strong seas (20 knots in 5 meters seas and 45 knots of wind a 6 sea state); pass smoothly the waves, are safe, maneuverable, stable and predictable. And are self righting. You have the feeling of reading the claims of an ad of a miraculous Florida built yacht for italians from Chicago, but it's verified by many pros.
    Fishermen love his boats from 9 to 23 meters, finding them safe with sweet movements, having plenty of room and good ergonomics.
    All the guys involved in rescue who have tried his rescue boat for the SNSM (Société Nationale de Sauvetage en Mer) in all conditions love it and praise the NA and the small old provincial shipyard (25 persons) which builds it. At the difference of many self righting boats, it does not roll, does not need anti roll keels like some designs and behaves nicely, while being able to keep a very good speed, excellent passage in the waves and safe maneuvering in the worst of the seas. Again the american ad for a Florida boat.
    The SNSM is so happy that they have made the plans of buying several (at least 10 or 15) over the years. It's a lot of work for the shipyard and the NA. And on lot of money for the SNSM. We are all giving money for these new boats as our neoliberal government does not bother about safety for seamen, so the budgets about maritime safety are now ridiculous, many lighthouses are falling in derelict and the French Navy is struggling to keep the high sea tugs.

    Personally I think that this signature bow is only the very visible feature, but the job resides really in the water lines, the repartition of the volumes and the placement of the centers. In fact it's the sum of all these features that gives the qualities of his boats. As it's visible during the self righting trial the under lines are smooth and deceptively simple at first sight.

    So it was for me a big surprise see this so "frenchy" polyhedric bow of a provincial NA from Brittany on an italian 140 meters warship.
    Italy has plenty of good NA and NE, plus a long tradition of ship building with pretty good shipyards. As the Italian Navy works on a shoestring budget, they can't throw money in an adventurous design. If after the first frigate and the trials the Italian navy decided to finance a total of 10 almost sister ships (6 already built and sailing, the seventh in construction, 3 other planned) I guess that the ship has some qualities, does well its job and probably that this bow must offer some advantages that overcome its complication of design and cost of realisation.
     
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  11. jehardiman
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    jehardiman Senior Member

    Actually, seems to me the bow is extended to maintain LWL. Here is a stern photo...look where the boot topping is painted. And the shafts make me shudder also.
    [​IMG]
     
  12. Ilan Voyager
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    Ilan Voyager Senior Member

    Mediterranean Sea is not a relatively calm sea. The winter can be pretty harsh and nicely windy. The worst is the short sea with pretty steppy waves that transforms a warship in a shaky drum (I have lived it). But surely it's not the North Atlantic with the depressions following one after another and where you can learn what is pure terror even on a warship.
    The main purpose of Italian Navy is to survey their very long coast and to be present at some nevralgic places.
    Besides a lot of smuggling and illegal fishing, politically the Mediterranean Sea is far from quiet.
    You have Libya caught in a civil war with lots of refugees trying to cross, you have Syria caught in a civil war, plus Americans, Russians, Turks, Daesh remnants and I forget many others. Add the refugees trying to reach Greece from Turquia. The Russian Navy zoning in front of the Middle East. The American Fleet zoning close to the Russians and trying also to intimidate the Turkish.
    The Italians are just in front of Tunisia and Libya, receive thousands of refugees, bury thousands of drown refugees who arrive on the coasts of Sicilia, and have across the Tyrrhenian Sea the delicate remnants of the former Yugoslavia, plus again refugees from these countries and Albania.
     
  13. Ilan Voyager
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    Ilan Voyager Senior Member

    I've dozens of similar shafts on warships and the 5 blades propellers look rather classical. The bow seems more designed for getting more volume underwater just at the bow while lessening the bow drag wave than simply lengthening tle LWL. You do not go in all this complexity in the bow because it's fancy, and it would be simpler and cheaper to add a couple of meters of length with a straighter bow. Only guessing as I do not know anybody in the Italian Navy. Probably also to minimize the effects of the step waves in the short seas, also guessing. But it has a purpose for sure and I bet the Italian NA have made plenty of tank tests in all the imaginable configurations to validate the design.
     
  14. jehardiman
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    jehardiman Senior Member

    Now that I did some digging into the numbers (dimensions, weights, and volumes) and the Italian Navy SOR, the bow is primarily for weight savings on LWL, and max smooth water speed, nothing else. The boot topping and transom tunnels are the giveaway once you see the SOR. They expect squat to lift the bow clear. Because this ship class is to replace all of Italy's large patrol combatants as well as meet green-cruize and minimum manning, a lot of compromises were built into the hull.
    Wayback Machine https://web.archive.org/web/20171022040825/http://www.gsweek.it/wp-content/uploads/02_SIMONE-compressed.pdf
     
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  15. Ad Hoc
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    Ad Hoc Naval Architect

    A colleague of mine knows the original designer of the French boats. He said very openly, the reason why they put the bow extension on was.... the original design once launched was bow heavy and trimmed badly under speed. The quick simple solution, add more buoyancy at the bow to lift her...as JEH notes too.

    But since those days, the "myth" has grown... as these things always do... :confused:

    It is just adding waterline length and all the hydrodynamic benefits that any hull gains from doing as such.
     
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